Heartworm Disease in Dogs
May 27, 2016
Many dog owners have heard of heartworm disease but
may not fully understand how the disease develops. Some owners may
even question if an annual test for heartworm disease is necessary.
Dr. Sonya Wesselowski, clinical assistant professor of cardiology
at the Texas A&M College of Veterinary Medicine &
Biomedical Sciences, said testing for heartworm disease and
administering regular monthly heartworm medication is crucial.
“All dogs should be tested for heartworm disease every year at
their annual wellness visit,” Wesselowski said. “Additionally,
patients that have not previously been on heartworm prevention or
those that have had a lapse in their heartworm prevention should be
tested immediately, then again in six months, and annually
To help dog owners understand why preventing heartworm disease
is so important, Wesselowski explained how the disease develops.
“Heartworm disease is caused by a long, thin worm known as
Dirofilaria immitis,” she said. “Heartworms live
within the heart, lungs, and blood vessels and can cause damage in
these areas. This damage can lead to lung disease, elevated blood
pressure inside the lungs, and even heart failure. In some cases,
other organs in the body are affected as well.”
“The first step in the heartworm lifecycle occurs when a
mosquito bites an infected dog,” she continued. “The mosquito
ingests the microscopic offspring of the adult heartworm known as
microfilaria. These microfilaria then mature inside the mosquito
over ten to 14 days and become infective larvae that can be
deposited onto the skin of another animal when the mosquito bites
again. The larvae enter their new host through the bite wound left
by the mosquito and develop into adult heartworms in about six
months. The adult heartworms can then live for five to seven years
in the infected dog.”
Signs of heartworm disease in dogs range from a mild cough and
decreased exercise capacity to heart failure and the accumulation
of abdominal fluid. In severe cases, heartworms can cause caval
syndrome, a rapidly progressing fatal disease that blocks blood
flow within the heart. Caval syndrome causes symptoms such as
labored breathing, collapse, and dark-colored urine.
The thought of heartworms infecting Fido may sound like a
nightmare. Thankfully, treatment is available. However, according
to Wesselowski, resolution of a heartworm infection is not a quick
and easy process. “If a dog tests positive for heartworms, the
first step is to confirm the diagnosis with a follow-up test,” she
said. “Once the diagnosis is confirmed, additional laboratory and
imaging tests will help your veterinarian stage the severity of the
disease and develop an appropriate treatment plan. Treatment
involves multiple oral medications for at least one month, followed
by a set of several injections to kill the adult heartworms. Strict
exercise restriction and kennel confinement is essential throughout
the entire course of treatment to reduce the risk of serious
complications that can be associated with resolving the heartworm
Wesselowski also stressed that the treatment of heartworm
disease is expensive for pet owners and taxing for affected pets.
The heartworms can also cause long-term damage to the heart and
lungs that remains even after the heartworm infection is
successfully resolved. This means that when it comes to heartworm
disease, prevention is key.
“Administration of regular monthly heartworm preventatives is
crucial to prevent heartworm disease and to avoid the stress,
expense, and potential complications that can be associated with
heartworm treatment in our beloved family pets,” Wesselowski
Pet Talk is a service of the College of Veterinary
Medicine & Biomedical Sciences, Texas A&M University.
Stories can be viewed on the Web at vetmed.tamu.edu/pet-talk.
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